OA equipment including electrophotographic apparatus and electrostatic recording apparatus such as copiers, facsimile equipment, printers are constituted of various parts, and blades, rollers and belts are essential parts playing such a roll as charging, developing, transfer, fixation, static electricity elimination, cleaning, paper feeding, transportation or the like in electrophotographic processes. These parts are mostly made of polyurethane materials and, in many cases, they must be provided with a conductivity of about 104 to 1012 Ω·cm from the functional viewpoint.
The measures that have so far been taken for providing polyurethane members for OA equipment parts with conductivity comprise, for example, molding polyurethane materials obtained by adding and dispersing an electronically conductive substance such as carbon black, a carbon fiber, carbon flakes, a metal powder, a metal fiber, metal oxide whiskers, to and in polyurethanes, or by adding and dissolving an ionic conductive substance such as a perchlorate or an ammonium salt, to and in polyurethanes.
However, it is very difficult to provide such moldings wholly and uniformly with stable conductivity by the method comprising addition and dispersion of carbon black or a metal powder, for instance, since a slight deviation in the amount of addition of such a substance, slight changes in conditions such as material temperature, molding temperature, molding time and, further, the use of a different molding method result in changes in conductive path morphology, hence in great variations in conductivity, in particular in the volume resistivity range of 106 to 1011 Ω·cm. Further, the addition of such substances to polyurethane materials sometimes leads to a marked increase in system viscosity, making molding thereof difficult and impairing the mechanical properties of moldings themselves. Furthermore, these substances are generally higher in specific gravity than polyurethanes, so that these substances sometimes settle during storage or molding, leading to failure to attain the desired level of conductivity. Moreover, with the conductive polyurethanes obtained by such methods, the electric resistance is highly dependent on the voltage applied and the electric resistance changes markedly during continuous energization, hindering the development of high-performance electrophotographic apparatus and electrostatic recording apparatus.
On the other hand, for attaining a desired level of conductivity, in particular a volume resistivity in the range of 105 to 1010 Ω·cm, by the method involving addition and dissolution of an ionic conductive substance such as a perchlorate or an ammonium salt, it is necessary to add the ionic conductive substance in a relatively large amount. This produces problems; not only the cost increases but also the mechanical properties of moldings themselves are weakened and/or the ionic conductive substance bleeds out or blooms on the surface of moldings to contaminate photoconductors, papers and the like. Furthermore, since such substances are generally used in the form of masterbatches prepared by dissolving them in a highly hygroscopic substance such as polyethylene glycol, only those moldings which readily absorb moisture and show great changes in conductivity upon temperature and humidity changes can be obtained. Furthermore, the moldings obtained show a strong tendency toward great changes in resistance during continuous energization.